Predation by Ermine and Long-tailed Weasels on Duck Eggs

Ermine (Mustela erminea) and long-tailed weasel (M. frenata) predation
on duck eggs was studied at Union Slough National Wildlife Refuge, Kossuth County,
Iowa, in 1984-85. Captive individuals of both species ate 2-4 duck eggs at a
rate of 0.5-2.0 eggs per trial-day; all eggs were moved but some were not opened.
One hole, ringed with small fragments and "bite-outs", was made in all eggs
opened by captive weasels. In the field, the appearance of opened eggs, the
pattern of egg loss, and the amount of nest bowl disturbance were used to determine
the number of nests depredated by weasels. Egg loss at nests depredated by weasels
generally occurred over several days; nest bowl disturbance was minimal and
most hens did not abandon their nests until over half their eggs were taken.
Of 263 upland duck nests that failed due to predation, 38 had eggs taken by
weasels and 27 of the 38 failed solely because of weasels. Weasels also took
eggs from at least 5 of 20 nests that lost 1-7 eggs before the remaining eggs
hatched. Because 12 of 13 weasels captured were ermine, most depredation of
nests by weasels during the study probably was by ermine.
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